Liquid crystal display devices are used as display devices of large screen TVs and also as small display devices of display sections or the like of mobile phones. TN (Twisted Nematic)-mode liquid crystal display devices widely used conventionally have a relatively small viewing angle. Recently, liquid crystal display devices of an IPS (In-Plane-Switching) mode and a VA (Vertical Alignment) mode having a wide viewing angle are produced. Among such wide viewing angle modes, the VA mode can realize a high contrast ratio and thus is adopted in many liquid crystal display devices.
As one type of VA mode, an MVA (Multi-domain Vertical Alignment) mode is known in which a plurality of liquid crystal domains are formed in one pixel area. In an MVA-mode liquid crystal display device, an alignment regulation structure is provided in at least one of a pair of substrates which face each other while having a vertical alignment liquid crystal layer therebetween. The alignment regulation structure is, for example, a linear slit (opening) provided in an electrode or a rib (projection structure) provided on an electrode. Owing to the alignment regulation structure, an alignment regulation force is provided from one surface or both of two surfaces of the liquid crystal layer, and thus a plurality of liquid crystal domains (typically, four liquid crystal domains) having different alignment directions are formed. In this manner, the viewing angle characteristic is improved.
It is known that the VA mode has a disadvantage that the display quality as viewed in a front direction and the display quality as viewed in an oblique direction are conspicuously different from each other. Especially in gray scale display, when an adjustment is made such that the display has an appropriate display characteristic when viewed in the front direction, the display characteristic such as the tinge or the gamma characteristic when viewed in an oblique direction is significantly different from the display characteristic when viewed in the front direction. The optical axial direction of a liquid crystal molecule is the direction of a longer axis thereof. In gray scale display, the optical axial direction of the liquid crystal molecule is tilted by a certain degree with respect to main surfaces of the substrates. When the viewing angle (viewing direction) is changed in this state such that the display is viewed in an oblique direction which is parallel to the optical axial direction of the liquid crystal molecule, the display characteristic is significantly different from the display characteristic as viewed in the front direction. Specifically, a display image viewed in an oblique direction appears to be whitish overall as compared with a display image viewed in the front direction. Such a phenomenon is called “white floating”. When, for example, a human face is displayed, the facial expression or the like may be recognized with no unnaturalness in the front direction. However, when viewed in an oblique direction, the face may appear to be whitish overall, and the subtle gray scale representation of the color of the skin is spoiled.
In order to alleviate the white floating, it is known to divide one pixel into a plurality of (typically, two) sub pixels and to apply different effective voltages to the sub pixels. In such a liquid crystal display device, the gray scale characteristic of the sub pixels is adjusted such that the display quality as viewed in an oblique direction is not lower than the display quality as viewed in the front direction (see, for example, Patent Documents 1 through 3).
FIG. 8 shows a liquid crystal display device 700 disclosed in Patent Document 1. In the liquid crystal display device 700, two sub pixel electrodes 724a and 724b are connected to different source bus lines Ls via different TFTs 730a and 730b, respectively. The liquid crystal display device 700 is driven such that the two sub pixel electrodes 724a and 724b have different potentials from each other. Since the potentials of the two sub pixel electrodes 724a and 724b are different like this, areas of a liquid crystal layer corresponding to sub pixels Spa and Spb are supplied with different voltages from each other. Therefore, the sub pixels Spa and Spb have different luminances from each other. As a result, the white floating is alleviated.
FIG. 9 shows a liquid crystal display device 800 disclosed in Patent Document 2. In the liquid crystal display device 800, two sub pixel electrodes 824a and 824b are connected to the same source bus line Ls via different TFTs 830a and 830b, respectively. The two sub pixel electrodes 824a and 824b are respectively connected to storage capacitance bus lines Lcsa and Lcsb via storage capacitances CCa and CCb. The liquid crystal display device 800 is driven such that the potentials of the sub pixel electrodes 824a and 824b are different in accordance with different storage capacitance signal voltages supplied to the different storage capacitance bus lines Lcsa and Lcsb. Since the potentials of the sub pixel electrodes 824a and 824b are different like this, sub pixels Spa and Spb have different luminances from each other. As a result, the white floating is alleviated.
FIG. 10 shows a liquid crystal display device 900 disclosed in Patent Document 3. In the liquid crystal display device 900, two counter electrodes 944a and 944b which may have different potentials from each other are provided for one pixel electrode 924. Since the potentials of the counter electrodes 944a and 944b are different from each other like this, areas of the liquid crystal layer corresponding to the sub pixels Spa and Spb are supplied with different voltages from each other. Therefore, the sub pixels Spa and Spb have different luminances from each other. As a result, the white floating is alleviated.